The spill occurred near the Arkadelphia Road exit at about 7 p.m. that night. Birmingham police were told that a second 18-wheeler knocked into the chemical-carrying one, which caused the spill. The driver told police the second truck fled the scene.

Birmingham police spokesman Lt. Sean Edwards said they are still investigating the story about a second truck, but there is no active search for the driver.

The truck belongs to Industrial Chemicals Inc., a chemical and waste disposal company headquartered in Vestavia. The company confirmed this to AL.com. However, the proper personnel to comment were not available.

The truck's contents were confirmed by Birmingham Fire and Rescue Battalion Chief C.W. Mardis. He said there was toluene, hydrogen peroxide, hydrofluoric acid and a container of sulfuric acid.

The leaking hydrogen peroxide heated up once it came into contact with the air, he said. Its subsequent contact with the toluene - a flammable additive that is used in gasoline among other things - likely caused the truck to catch fire after the truck stopped, he said.

"At that point we had so many chemicals to deal with, it was a very dangerous situation," he said.

All of the involved chemicals can be toxic to inhale. Mardis said they could naturally dissipate in the air, but the concentrated levels made evacuation necessary to ensure public safety.

Once the fire was out, cleanup crews from Industrial Chemicals could get to work. The evacuation was lifted after a few hours.

Mardis said the fire units left at about 8 .m. Thursday. Some of the cleanup crews remained for a while longer.

No one was hurt throughout the incident. Besides the evacuation, the main concern was the traffic because of the closure of I-59/20.

"The operation went really smoothly. I think all in all it was a good turnout with good results," Mardis said.

All of these components can be toxic, which prompted the half-mile evacuation.

Other responding agencies included the Jefferson County Emergency Management Agency, Alabama Department of Transportation and Alabama Department of Environmental Management.

Jody Hodge, an emergency management officer with Jefferson County EMA, said they mostly deal with fuel leaks. They do get called for occasional chemical spills, although not often.